Recently, a non-contact power supply apparatus (contactless power transmission system) for transmitting electric power in a non-contact (contactless) manner has been developed instead of direct electrical connection.
FIG. 19 is a circuit diagram of an essential part of conventional non-contact power supply apparatus 100. Non-contact power supply apparatus 100 includes power receiver 101, power transmission controller 119, and power transmitter 120.
When power transmission is continued in the state where metallic foreign object 129 is interposed between power transmitting coil 123 and power receiving coil 127 in non-contact power supply apparatus 100, eddy current flowing through metallic foreign object 129 generates heat. To address this problem, the following method is devised. Whether metallic foreign object 129 is present between power transmitting coil 123 and power receiving coil 127 is detected by signal processing. The method is detailed below.
Power receiver 101 includes the following elements: load modulation transistor 103; rectifying circuit 104; power supply control transistor 105; power receiver side control circuit 107; low drop-out (LDO) regulator 109; and power receiving coil 127. Load modulation transistor 103 performs load modulation. Power supply control transistor 105 controls power supply. Power receiver side control circuit 107 controls load modulation transistor 103 and power supply control transistor 105.
The voltages at the input end and the output end of low drop-out regulator 109 are input to power receiver side control circuit 107 through signal lines 111, 113, respectively. Power receiver side control circuit 107 detects the state of load 115 by measuring the voltage across low drop-out regulator 109. Load 115 is formed of battery 117 and charge controller 116.
Power transmitter 120 includes power transmitting coil 123 and power transmitting part 124. Power transmission controller 119 includes waveform detecting circuit 121, voltage detecting circuit 122, power transmitter side control circuit 125, and driver control circuit 126.
In power transmission controller 119, waveform detecting circuit 121 detects the peak value of the amplitude of the induced voltage of power transmitting coil 123. As a result, power transmitter side control circuit 125 detects fluctuations in the load of power receiver 101.
Power receiver 101 performs load modulation during normal power transmission, and transmits foreign object detection signal PT1 from power receiving coil 127 to power transmitter 120. In response to this signal, power transmitter side control circuit 125 measures a change in the load of power receiver 101. When foreign object detection signal PT1 cannot be received, power transmitter side control circuit 125 determines that metallic foreign object 129 is present and stops normal power transmission. With this configuration, metallic foreign object 129 between transmitting coil 123 and receiving coil 127 is detected.
As a prior art document related to the above technology, Patent Literature 1, for example, is known.